Best Operating Practices for Pollution Prevention in Electroplating By: Frank Altmayer, MSF, Consultant and Technical Education Director, AESF Foundation/NASF Pollution Prevention in Electroplating Focus Areas: • Masking • Racking • Process Solutions • Rinse Systems • Maintenance and Housekeeping BOP of Process Solutions Focus on Maintenance • Accurate and frequent solution analyses Use of statistical process control (SPC) • Removal of dropped parts • Deionized water use • Bus bar maintenance • Control of operating parameters • Filtration • Use of inert anodes • Contamination removal BOP of Process Solutions Analytical Control of Process Solutions: Constituent Concentration ±2% Optimum Level + 10% Time Selecting Masking Materials Factors to Consider: • The amount of labor/skill required • Part geometry and size/weight • The chemical resistance of maskant • The chemical resistance of adhesive • The temperature limitations of maskant • Cleaning requirements • Physical resilience of maskant • Ability to seal complex surfaces • Spec Requirements • Ease of maskant removal • Cost to purchase and disposal of residuals UV Curable Masks Potential Applications: • Acid Based Stripping • Anodizing • Plating (including EN and Hard Chromium) • Chemical Milling Photo courtesy of • HVOF/Plasma Spray Dymax Adhesives & Light Curing Systems Inc. • Painting/Powdercoating • Blasting/Shot Peening/Vibratory Finishing UV Curable Masks Burn-Off Masking Resins • Best surface adhesion • Greatest resistance to heat/aggressive chemical solutions • Secondary heat curing capability • 900°F to 1400°F (~15 minutes) • Maskant is incinerated leaving no residue Peel-able Masking Resins • Good adhesion • Resilient enough for grit blasting, shot peening, acid cleaning, plating and anodizing • Removed through by peeling • Cured in a few seconds with UV light • Can be used in multiple process steps • Maskant waste is non-hazardous Photo courtesy of Dymax Adhesives & Light Curing Water Soluble Masking Resins Systems • Used in "dry" finishing processes such as grit blasting, grinding, shot peening, and plasma spraying • Maskant dissolves in hot water (140° - 180° F) and a spray wash or agitated/ultrasonic bath • Maskant completely dissolves in the water leaving no residue • 20% maskant in water has a pH of 7 UV Curable Masks UV Curing Systems System Factors • Spectral output of the lamp • Lamp intensity • Size/shape of part • Production rate Spot Lamps • Generate high intensity UV energy that is directed through a fiber or liquid filled light guide, typically 5-8 mm in diameter • Ideal for curing UV Masking Resins in cooling holes Photo courtesy of Dymax or sealing off core cavities Adhesives & Light Curing Systems Flood Lamps • For larger surfaces like airfoils and housings • Footprints up to 8" square. Note: When cured, the resin changes color (blue to pink for example) to indicate a complete cure. Reducing Mask Usage in Hard Chromium Plating Plated Surface Plating tank has no anodes Anode fixture for plating hydraulic part shown Solution may be pumped into Anode/cathode compartment during plating Assembly Anode Out-of-Tank Plating Plating Solution In Features: Plating Plating • May Eliminate Masking Solution Out Solution Out • Small solution volume required • High agitation velocities + - Higher CCE - Less pitting • Very High Plating Speeds • Uniform Thickness Hydraulic Cylinder, With No Drain Holes Parts Lost in Processing Chief Causes of Dropped/Lost Parts: • Poor Rack Maintenance • Poor Barrel Door Maintenance • Poor Operator Practices Prevention: • Preventative Maintenance • Inspection Program • Scheduled Removal Program Good Rack Maintenance Practices Broken Tips: • If 1 of 10 tips is broken = 10% loss in productivity Do not strip tips with pliers Damaged Coatings: Heavy Plating Buildup on Tips: • Ruptured coatings at the corners or the • Inspect for build-up on tips and bottom of a rack or at rack tips can cross- chemically strip excess contaminate all process solutions and will • Strip rack tips frequently corrode the splines • Remove damaged racks from service Good Rack Maintenance Practices Proper Rack Handling/Storage: Suspended racks from Do not store racks on the floor hooks to protect the PVC Hooks/Tank Bus: Inspect/clean inside of hooks frequently for better conductivity. Proper Rinse Practices Opportunities for Improvement: • Rinse agitation • Countercurrent rinsing • Air knives/sprays • Reactive rinsing • Proprietary plating barrels How Water Can Be Wasted Proper Rinse Practices Single vs. Counterflow Rinses: • Single rinses may be suitable for lines in sporadic use • Counterflow rinses dramatically reduce water usage in high volume production DI vs. Tap-water: • Use DI water for process solution make-up and replenishment • DI is not always the best choice Multiple Use Rinsing Acid Clean Clean Acid Rinse Rinse To Waste Exit of Acid Rinse Treatment must be 3” higher than Clean Rinse Reactive Rinsing Acid Clean Clean Acid Rinse Rinse To Waste Exit of Acid Rinse Treatment must be 3” higher than Clean Rinse Spray Rinses/Air Knives • Match spray pattern to part shape Quick change • Mix air with water to reduce consumption Flat-Narrow • Make spray nozzles easy to service • Spray over hot process tanks when possible Flat Broad • Use Low Pressure Blower Air, 15 psi • Air Should Be Highly Humidified Hollow Cone • Use De-Ionized Water to Avoid Nozzle Clogging • Design Nozzles for Optimum Full Cone Coverage Controlling Water Usage Inductive Loop • Turn back main valve • Install flow restrictors • Timer • Conductivity Controllers with Do not use inductive loop probe(s) Conductivity controller, with a variety of probes • Flow Meters • Monitor using rotameters Flow Restrictor Process Ventilation Downdraft: • Collects Condensation • Collects Mists • Creates Nice View • Ineffective for Very Hot Processes Downdraft Ventilation System Updraft: • Condensation/Mist Returned to Process • More Effective on Very Hot Tanks Part-time Updraft • Major reduction in exhausted air Part-time Updraft Ventilation System Proper Ventilation Practice Eliminate ventilation system obstructions: Bus bar blocks Ventilation and is corroded by mist Bus bar blocks push air Hard Chromium Plating Tank Tank Liner Design/Maintenance • Most Common Hard Chrome Liners: - Standard Rigid PVC (Koroseal®) - High performance PVC (HP Koroseal®) • Conductive: - Lead alloy - Titanium Damaged Koroseal® liner after 9 • Non-Conductive: months of service in hard chromium tank (no “skirt”) - CPVC - Rigid PVC + HP Koroseal® - Halar fluorocarbon - PVDF (Kynar®) - Polypropylene - High density polyethylene - Acid brick Note: annual spark test is highly recommended Tank Insulation • Heavily used tanks: − Insulation may prevent efficient cooling of solution • Infrequently used tanks: − Insulation conserves energy Installation of Polyurethane Insulation Use “C” Clamp To Hold Outer Shield In Place During Foaming Caulk Between Tank Lip & Outer Shield Lip Solidified Foam Holds Shield In Place 1” of Polyurethane Foam Insulated Hard Chrome Tank Injection Hole In PVC Outer Shield. Cover After Injection Partial View Of Wood or Plastic Tank Wall Spacer Control Operating Parameters Higher Operating Temperature • Lowers viscosity • Increases evaporation • May increases plating efficiency Eductor Agitation • May increase plating efficiency • May improve plating distribution • Reduces air emissions • Increases anode efficiency Higher Current Density • May increases plating efficiency Air (top) vs. Eductor agitation In-Tank and Out of Tank Filtration In-Tank Filter Out of Tank Filter Notes: Install Out of Tank Filters in Trays Use Re-usable Filtration Media Anode Bags • Improper bags and bags in poor condition generate waste • Inspect frequently • Replace annually or every 2 years • Use the correct material and weave Example, for bright nickel plating: • Cast, Rolled Carbon, Electrolytic Anodes – Cotton (96 warp x 64 weft) 8 oz/yd2 Photo by F. Altmayer • Cast, Rolled Carbon, Electrolytic, S Rounds – Cotton Flannel (64 x 40) 12 oz/yd2 Double Bagging: • Inside: One of the above, • Outside: – Dynel (38 x 29) 6.25 oz/yd2 or – Dacron (67 x 47) 4.75 oz/yd2 Wikipedia Illustration Remove Contamination from Metallic: Plating Solutions • Low current density electrolysis • Chemical Treatments – Hydrogen peroxide – pH adjustment – Polysulfides • Ion Exchange/Membrane Technologies Organic: – Activated carbon adsorption – Hydrogen peroxide treatment – Prevention is better than treatment Carbonates: – Chilling – Chemical precipitation BOP of Process Solutions Dragout Reduction: • Use of dragout tanks • Installation of drain boards / hang bars • Increase dwell time • Reduce removal rate • Optimum racking & part geometry • Use of wetting agents • Reduce viscosity of solution • Installation of air knives • Proper rack / barrel maintenance Proper Use of a Drag-out Rinse Hot Processes: Optimum Sequence: 1. Drag-in 2. Plate 3. Drag-out 4. Rinse Cold Processes: Use DI/DO System Reducing Drag-out Options: • Optimize part withdrawal rate: − 15 - 25 ft/min • Optimize dwell time before rinsing: − 15-20 seconds − Exceptions: Nickel Plating, Chromates • Reduce surface tension of the solution • Increase the operating temperature of the solution • Decrease the concentration of solution ingredients More BOP on Barrels • Holes should be tapered (bigger on outside) • Holes should be as large as possible but less than 30% of wall area • Eliminate Plugged holes • Maintain Dangler Cable Insulation • Dangler Sleeve May Be Feasible in High drag-out rate barrel